1. Field of the Invention
The present invention relates to motor devices used in magnetic disk drives, and in particular, relates to a motor device in which decentering during disk rotation can be suppressed.
2. Description of the Related Art
FIG. 11 is a perspective view of a bearing unit 50 which is a component of a motor device to be mounted on a magnetic disk drive for a floppy disk (FD).
The bearing unit 50 includes a cylindrical bearing 51 and a flange 53 provided integrally with the periphery of the cylindrical bearing 51. The flange 53 is provided with U-shaped grooves 54 at the longitudinal ends of the flange 53 for positioning the bearing unit 50 on a mounting base. The flange 53 is also provided on an upper face 53a thereof with a pair of rectangular projections 55 at one of the longitudinal ends provided with the grooves 54 of the flange 53. The cylindrical bearing 51, the flange 53, and the projections 55 are integrally formed with each other by a method, such as by die-casting or sintering.
The bearing unit 50 receives a rotational shaft (not shown) in a coupling hole 52 of the cylindrical bearing 51. Thus, the rotational shaft is rotatably supported. The rotational shaft is provided with a rotor, fixed thereto, having a magnet, the rotor being rotatable integrally with the rotational shaft.
The bearing unit 50 is provided with a core unit fixed to the upper face 53a of the flange 53. The core unit is disposed inclined by being supported by a part of the upper face 53a and the projections 55 of the flange 53. The core unit is thus supported slightly inclined with respect to a plane perpendicular to the rotational axis.
When the core unit is fixed to be inclined on the bearing unit 50, decentering, or surface misalignment, that is, wow and flutter due to precession movements of the rotational shaft can be suppressed, whereby tracking errors due to off-tracking of a head from recording tracks on the disk can be avoided, the off-tracking being caused by the decentering.
However, a problem has been found in the above-described known motor device, which is described below.
During manufacturing, the above-described bearing unit 50 is proceeded in a sizing process in which the inner diameter of the coupling hole 52 is set by press-fitting a shaft or the like into the hole so as to obtain the accuracy in size. However, the sizing cannot be performed at a high accuracy when the projections 55 are formed on the upper face 53a of the flange 53, as shown in FIG. 11, because the sizing is performed with the upper face 53a of the flange 53 being as a reference, thereby producing decentering of the rotational shaft; therefore, high on-tracking accuracy cannot be ensured.
Moreover, the bearing unit 50 having a complex shape including the projections 55 is made of a specified material to be formed integrally with the flange 53, thereby increasing processing costs, whereby overall manufacturing cost is increased.
Accordingly, it is an object of the present invention to provide a motor device in which high sizing-accuracy is possible and which can be manufactured at a low cost.
To this end, according to a first aspect of the present invention, a motor device comprises a base, a bearing unit fixed to the base, a core unit including coils provided around cores to be fixed to the base side, a rotational shaft rotatably supported by the bearing unit, a rotor fixed to the rotational shaft, and a magnet fixed to the rotor and opposing the core unit. The bearing unit includes a flange extending along the base and a spacer disposed on the flange and having an inclined surface. The core unit is placed on the inclined surface of the spacer, whereby the core unit is disposed inclined with respect to an upper face of the base.
With this arrangement, sizing can be performed, before the spacer is placed on the flange and is fixed thereto, by using an upper surface of the flange as a reference, thereby enabling a highly accurate sizing.
According to the present invention, it is not necessary to integrally form a bearing unit of a specified metallic material, which has a complex shape by having projections as in a known bearing unit, thereby reducing costs, such as machining costs, of the motor device.
According to a second aspect of the present invention, a motor device comprises a base, a bearing unit fixed to the base, a core unit including coils provided around cores to be fixed to the base side, a rotational shaft rotatably supported by the bearing unit, a rotor fixed to the rotational shaft, and a magnet fixed to the rotor and opposing the core unit. The bearing unit includes an individual flange mating with a bearing at the periphery of the bearing, the flange having a bottom surface perpendicular to the rotational shaft and an upper surface inclined with respect to the bottom surface. The core unit is placed on the inclined upper surface of the flange, whereby the core unit is disposed inclined with respect to an upper face of the base.
With this arrangement, sizing can be performed by using the periphery of the bearing as a reference before the bearing is mated with the flange, thereby enabling highly accurate sizing. Moreover, the bearing can be made with a simple straight cylindrically formed material, thereby reducing the manufacturing cost.
According to a third aspect of the present invention, a motor device comprises a base, a bearing unit fixed to the base, a core unit including coils provided around cores to be fixed to the base side, a rotational shaft rotatably supported by the bearing unit, a rotor fixed to the rotational shaft, and a magnet fixed to the rotor and opposing the core unit. The motor device further comprises a positioning member for positioning the core unit on the base, and a supporting member formed integrally with the positioning member. The core unit is disposed inclined with respect to the base by being supported by the bearing unit and an upper surface of the supporting member.
With this arrangement, sizing can be performed by using a surface perpendicular to the rotational shaft as a reference before the supporting member is provided, thereby enabling highly accurate sizing. The supporting member is designed to have a surface for supporting the core unit at a level, for example, higher than that of the bearing unit, whereby the core unit is supported inclined in a given direction.
The supporting member is preferably supported by the bearing unit at a bottom surface of the supporting member. For example, the supporting member may include a tabular protrusion protruding from a positioning member toward the bearing unit, thereby providing the supporting member with resiliency so as to be vertically deflectable, whereby the supporting member is deflected when the core unit is loaded thereon, so that the supporting member is supported by the bearing unit.
According to the present invention, by the magnetic attraction between the magnet provided on the rotor and the core unit which is fixed inclined to the bearing unit, the rotor is inclined in the same direction as the core unit, thereby tilting the rotational shaft. The rotational shaft is urged to one side of the coupling hole with which the rotational shaft is rotatably coupled, whereby decentering of the rotational shaft is prevented, thereby suppressing tracking errors.